Inhaled sulfur dioxide as well as injected or ingested sulfite reacts with certain disulfides in mammalian plasma cleaving S-S bonds and producing S-sulfonate groups. The kinetics of the formation and clearance of plasma S-sulfonate in laboratory primate species will be studied and compared with similar studies on rabbits, mice, and rats. A major aim of the proposed research is to elucidate the mechanism of clearance of protein S-sulfonate from the plasma, especially with regard to the function of diffusible thiol groups. The importance of cysteine S-sulfonate in plasma S-sulfonate clearance and the potential of this system (cysteine plus protein S-sulfonate yields reversibly cysteine S- sulfonate) for functional sulfite transport to tissues outside of the blood stream will be investigated by various techniques including the use of 35S tracer. Identification of plasma proteins affected by in vivo sulfitolysis will be undertaken with the aid of 35SO3. The ultimate objective is the detection of toxic effects due to structural alteration of proteins and possible resultant functional changes. Sulfite oxidase, an enzyme which detoxifies sulfite by oxidation to sulfate, is especially rich in mammalian liver. This enzyme should play a major role in the determination of the availability of sulfite for reacting with disulfide bonds in plasma and other tissues. The correlation between hepatic sulfite oxidase activity and plasma S- sulfonate levels will be studied in several species.